1. Field of the Invention
The present invention relates to a space for fabricating a semiconductor device or a liquid crystal display device, and more particularly, to a structure of a clean room system having improved uniformity of air flow in a substantially vertical direction within a fabrication space.
2. Description of the Related Art
Development of TFT-LCD technology and its application have been accelerated with increased size and resolution. Presently, growth of productivity and low price are important factors for a product. To achieve this, cooperation between manufacturers, related material industries and fabrication equipment providers is required for simplification of the fabrication process and improvement in yield.
The fabrication process of a TFT-LCD panel can be divided into a TFT array process for forming switching devices to apply a signal of a pixel unit, a color filter process for forming R, G and B color filters to implement colors, and a liquid crystal process for forming a liquid crystal layer between a thin film transistor substrate and a color filter substrate. The liquid crystal display device formed by such a process can easily become defective due to fine dust or particle generated during the process. As a result, preventing contamination is crucial to reduce cost, to achieve high yield, and to efficiently produce a liquid crystal display device. Staff, equipment, facility (including clean room), and chemicals are a major cause of fine particle contamination. Especially, particles coming from staff and the clean facility are major contaminants. Thus, an extremely clean fabrication space (referred to as a ‘clean room’, hereinafter) is required for manufacturing a liquid crystal display device.
FIG. 1 illustrates the structure of a related art clean room system having three stories. As shown in FIG. 1, the three-story clean room system 100 includes a clean room 10 in which a fabrication process is substantially performed, lower and upper spaces (a and b) provided at upper and lower levels of the clean room 10, and dry coils 18a and 18b positioned at both sides of the clean room 10 and working as an air flow ascending passage. Equipment (for example, deposition equipment or etching equipment) for fabricating a liquid crystal are disposed in the clean room 10, and a fan filter unit 15 for supplying an air stream into the clean room 10 is provided at the ceiling of the clean room 10.
The related art clean room system 100 constructed as described above maintains cleanliness through independent air circulation in the clean room disposed in each floor. Namely, when an air stream is supplied from the lower space (a) of the first clean room 10a to the upper space (b) of the first clean room 10a, the air stream passes through the fan filter unit 15 disposed at the upper side of the first clean room 10a to form a vertical air stream inside the first clean room 10a. The vertical air stream comes into the lower space (a) of the clean room 10a after passing through the bottom plate 17 of the first clean room 10a, and then, ascends to the upper space (b) of the first clean room 10a through the dry coils 18a and 18b formed at both sides of the first clean room 10a. The air stream that has come in the upper space (b) moves into the first clean room 10a again through the fan filter unit 15 and forms a vertical air stream therein, and then, is discharged to the lower space (a) of the clean room 10a. Air stream circulation of the second and third clean rooms 10b and 10c is made in the same manner as in the first room 10a. 
The related art clean room system 100 repeats air flow circulation by raising an air stream of the lower space (a) of the clean room 10 up to the upper space (b) through the dry coils 18a and 18b prepared at both sides of the clean room 10, thereby maintaining cleanliness.
However, in the clean room system 100, since the dry coils 18a and 18b, the passage of the air stream to the upper space (b) are disposed at both sides of the clean room 10, the air stream in the clean room 10 is not formed exactly vertically but inclined to the side. Thus, as shown in FIGS. 2A and 2B, since the air stream in the central portion of the clean room 10 is inclined to the side of the dry coils 18a and 18b, cleanliness cannot be properly maintained in the central portion of the clean room 10.